If I'm faced with one of these lunatics I'm going to tell them to go f'off in no uncertain terms. Me being a customer they'll have no recourse. The public needs to intervene in these situations because it is a no-win situation for the employee. These people need their entitlement run down hard.
I have always tried to support employees, when they are in the right, against morons like this as I had more than enough in my 25 years of managing.
I had one that stands out, in the early eighties I had a very busy MickeyD's during a Saturday breakfast I was rocking eight registers on the counter with customers eight deep. I got called up front for a customer complaint they said and found one of my counter girls crying because some karen(not what we called them) walked up past all the customers in line and demanded the girl sell her a coffee, my cashier explained that we take all customers in turn and she needed to wait at the end of the line. The woman tore into the sixteen year old calling her names and insulting her intelligence. I approached the woman and told her I didn't appreciate her abusing my employee and she pulled the 'customer is always right crap' to which I responded that she wasn't a customer and she would find the door behind her. I got applause from all the actual customers, even the ones who still weren't served because of the bitch. Now some of the customers starting callin the women abusive names as she left and I asked them to please not to as I didn't need any help getting fired. Sometimes less really is more.